Loop heat pipe

ABSTRACT

A loop heat pipe includes an evaporator and a tube hermetically connecting with the evaporator. The evaporator includes a metallic container and a wick structure disposed in an inner surface of the container. The wick structure includes a first wick portion thermally contacting the whole inner surface of the container and a second wick portion enclosed by the first wick structure and contacting with the first wick portion. A number of channels are defined between the first and second wick portions for receiving vaporized working medium. The tube communicates with the channels of the evaporator so that the vaporized working medium can flow from the channels into the tube.

BACKGROUND

1. Technical Field

The present disclosure relates to heat pipes and, more particularly, to a loop heat pipe having a good heat dissipation efficiency.

2. Description of Related Art

Loop heat pipes have excellent heat transfer performance due to their low thermal resistance, and are therefore an effective means for transfer or dissipation of heat form heat-generating components such as central processing units (CPUs) of computers.

A conventional loop heat pipe comprises an evaporator thermally connected with a heat-generating component and disposing a wick structure therein, a condenser thermally connected with a heat sink, a vapor line and a liquid line disposed between and connecting the evaporator with the condenser. The wick structure comprises a central portion with a chamber therein and a number of extending portions radially extend outwardly from a periphery of the central portion. The outmost ends of the extending portions of the wick structure thermally contact inner surface of evaporator. A predetermined quantity of bi-phase working medium is contained in the evaporator and the liquid line.

During operation of the loop heat pipe, the working medium in the extending portions of the wick structure absorbs heat from the heat-generated component and vaporizes. Thus, the vaporized working medium generates a vapor pressure which propels vaporized working medium towards the condenser via the vapor line. The vaporized working medium dissipates heat to the heat sink at the condenser and condenses to liquid thereat. The condensed working medium is then propelled through the liquid line and the evaporator in that order by the vapor pressure and by capillary action generated by the wick structure. The condensed working medium at the evaporator then evaporates and is condensed to liquid thus perpetuating the cycle. Because only the extending portions of the wick structure contact with the evaporator, an evaporation rate of the working medium is low. Thus, a heat dissipation efficiency of the loop heat pipe is low.

What is needed, therefore, is a loop heat pipe having a good heat dissipation efficiency.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of a loop heat pipe in accordance with a first embodiment of the present disclosure.

FIG. 2 is a cross-sectional view of an evaporator of the loop heat pipe of FIG. 1, taken along line II-II thereof.

FIG. 3 is a view similar to FIG. 2, showing an evaporator of a loop heat pipe in accordance with a second embodiment of the present disclosure.

DETAILED DESCRIPTION

Referring to FIGS. 1-2, they illustrate a loop heat pipe in accordance with a first embodiment of the present disclosure. The loop heat pipe comprises an evaporator 10 and a hollow tube 20 hermetically connects with opposite ends of the evaporator 10. A predetermined quantity of working medium (not labeled) is contained in the evaporator 10 and the tube 20. The working medium is usually selected from a liquid which has a low boiling point such as water, methanol, or alcohol. Thus, the working medium can be easily evaporated to vapor when it absorbs heat in the evaporator 10 and condensed to liquid when it dissipates heat.

The evaporator 10 comprises a container 11 and a porous elongated wick structure 13 attached on an inner surface of the container 11. The container 11 may be constructed from any suitable metallic, such as aluminum, copper or stainless steel. In this embodiment, each of the wick structure 13 and the container 11 has a cylindrical configuration.

Particularly referring to FIG. 1, the container 11 comprises a heat absorbing portion 112 and an enlarged extending portion 114 extending forwardly from a front end of the heat absorbing portion 112 along a central longitudinal axis of the heat absorbing portion 112. The heat absorbing portion 112 is used to thermally contact with a heat-generating component (not shown), such as a CPU (central processing unit) of a computer. A diameter of the extending portion 114 is larger than that of the heat absorbing portion 112. A vapor outlet 1121 is defined at a central portion of a rear end of the heat absorbing portion 112. A liquid inlet 1141 is defined at a central portion of a front end of the extending portion 114.

The wick structure 13 consists of porous structure, such as screen mesh, or fiber inserted into the container 11 and held against the inner surface of the container 11, or sintered powders combined to the inner surface of the container 11 using a sintering process. The wick structure 13 has a central longitudinal axis, which is coextensive with the central longitudinal axis of the heat absorbing portion 112 of the container 11. A receiving chamber 137 extends in the wick structure 13 along the axis thereof and from an open end 134 of the wick structure 13, which is near the liquid inlet 1141 to a closed end 132 near the vapor outlet 1121. The receiving chamber 137 extends along a partial length of the wick structure 13. The closed end 132 spaces a distance from an inner surface of the rear end of the absorbing portion 112 of the container 11. The open end 134 abuts against an inner surface of the front end of the extending portion 114 of the container 11. The receiving chamber 137 comprises a first chamber 1371 and a second chamber 1373 communicating with the first chamber 1371. The first chamber 1371 is near to the closed end 132 of the wick structure 13. The second chamber 1373 is near to the opening end 134 of the wick structure 13. A diameter of the second chamber 1373 is larger than that of the first chamber 1371. The second chamber 1373 functions as a compensation chamber for the first chamber 1371.

Particularly referring to FIG. 2, the wick structure 13 comprises a first wick portion 131 and a second wick portion 133. A porosity of the first wick portion 131 is larger than that of the second wick portion 133. In other words, a pore size of the first wick portion 131 is smaller than that of the second wick portion 133. The first wick portion 131 is annular. An outer surface of the first wick portion 131 thermally contacts with a whole inner surface of the container 11 to improve evaporation rate of the working medium in the first wick portion 131. The second wick portion 133 comprises a cylindrical central portion 1331 and a plurality of ribs 1333 radially extending from a periphery of the central portion 1331 to engage with an inner surface of the first wick portion 131. The receiving chamber 137 is defined in the central portion 1331. A cross-section of the rib 1333 is a sector. A width of the rib 1333 increases along a radially outward direction of the rib 1333. The outmost ends of the ribs 1333 abut against the inner surface of the first wick portion 131. The ribs 1333 and the first wick portion 131 are connected together. The ribs 1333 provide paths for the working medium to flow from the receiving chamber 137 to the first wick portion 131 to prevent the first wick portion 131 from drying. The ribs 1333 are spaced from each other. Thus, a channel 135 is defined between each two adjacent ribs 1333. The channels 135 extend along a longitudinal direction of the second wick portion 133 from position near the 1373 to the closed end 132 of the wick structure 13 and through the closed end 132. It is important that the channels 135 extend through the closed end 132 in order to enable vaporized working medium in the channels 135 to flow into vapor outlet 1121.

Opposite ends of the tube 20 connect with the vapor outlet 1121 and the liquid inlet 1141 of the evaporator 11, respectively. The tube 20 is made of metallic materials compatible with the working medium, such as aluminum, copper, or stainless steel. The tube 20 can be easily bent and deformed to a desirable configuration. The tube 20 comprises a vapor line 21 and a liquid line 22 communicating with the vapor line 21. Opposite ends of the vapor line 21 connect with the vapor outlet 1121 and the liquid line 22, respectively. The vaporized working medium flows through the vapor line 21 to the liquid line 22. Opposite ends of the liquid line 22 connect with the liquid inlet 1141 and the vapor line 21, respectively. The liquid working medium flows through the liquid line 22 to the liquid inlet 1141 of the evaporator 10.

During operation of the loop heat pipe, the working medium in the first wick portion 131 absorbs heat from the heat-generating component and vaporizes. The vaporized working medium flow through the channels 135 into vapor line 21 via the vapor outlet 1121. The vaporized working medium dissipates the heat via the tube 20 and condenses to liquid thereat. The condensed working medium is then propelled through the liquid line 22, the second chamber 1373 and the first chamber 1371 of the receiving chamber 137 in that order by the vapor pressure and by capillary action generated by the wick structure 13. The condensed working medium at the evaporator 10 then evaporates and is condensed to liquid thus perpetuating the cycle. A heat absorbing plate 30 thermally contacts with the vapor line 21 to absorb heat of the vaporized working medium to improve heat dissipating efficiency of the loop heat pipe. The heat absorbing plate 30 is made of a metal with a high heat conductivity, such as copper. The heat absorbing plate 30 functions as a heat sink for dissipating heat generated by the heat-generating component.

Referring to FIG. 3, it illustrates a loop heat pipe in accordance with a second embodiment of the present disclosure. A difference between the first and second embodiments is that the first and second wick portions 131 a, 133 a of the evaporator 10 a are formed by sintering a metal power. The first and second wick portions 131 a, 133 a have the same porosity.

It is to be understood, however, that even though numerous characteristics and advantages of the disclosure have been set forth in the foregoing description, together with details of the structure and function of the disclosure, the disclosure is illustrative only, and changes may be made in detail, especially in matters of shape, size, and arrangement of parts within the principles of the disclosure to the full extent indicated by the broad general meaning of the terms in which the appended claims are expressed. 

1. A loop heat pipe comprising: an evaporator comprising a metallic container and a wick structure disposed on an inner surface of the container, the wick structure comprising a first wick portion thermally contacting the inner surface of the container and a second wick portion enclosed by the first wick structure and contacting with the first wick portion, a number of channels defined between the first and second wick portions for receiving vaporized working medium therein, a receiving chamber being defined in the second wick portion for receiving liquid working medium therein, the receiving chamber being surrounded by the channels; and a tube hermetically connecting with two opposite ends of the evaporator, the tube having a vapor line communicating with the channels of the evaporator, the tube further having a liquid line communicating with the receiving chamber of the evaporator.
 2. The loop heat pipe as claimed in claim 1, wherein the first wick portion is annular.
 3. The loop heat pipe as claimed in claim 1, wherein the second wick portion comprises a central portion and a number of ribs extending outwardly from a periphery of the central portion, and the outmost ends of the ribs abut against the first wick portion.
 4. The loop heat pipe as claimed in claim 3, wherein the ribs are spaced from each other and each of the channels is defined between two adjacent ribs.
 5. The loop heat pipe as claimed in claim 4, wherein the receiving chamber is defined in the central portion of the second wick portion along a longitudinal direction of the central portion to receive the liquid working medium therein.
 6. The loop heat pipe as claimed in claim 1, wherein the container of the evaporator defines a vapor outlet and a liquid inlet located at the opposite ends thereof, and the wick structure has a first end spaced a distance from a portion of the inner surface of the container at which the vapor outlet is defined, and a second end abutting against a portion of the inner surface of the container at which the liquid inlet is defined.
 7. The loop heat pipe as claimed in claim 6, wherein the channels extend through the first end of the wick structure.
 8. The loop heat pipe as claimed in claim 1, wherein the first and second wick portions are connected together.
 9. The loop heat pipe as claimed in claim 1, wherein the first and second wick portions are formed by sintering a metallic powder.
 10. The loop heat pipe as claimed in claim 1, wherein the container of the evaporator comprises a heat absorbing portion and an extending portion extending outwardly from a lateral end of the heat absorbing portion, and the extending portion is larger than the heat absorbing portion.
 11. A heat pipe comprising: a metallic container; and a wick structure adhered on an inner surface of the container, the wick structure comprising: a first wick portion having an outer surface thereof thermally contacting with the container; and a second wick portion enclosed by the first wick portion and abutting against an inner surface of the first wick, a number of channels being defined between the first and second wick structures for receiving evaporated working medium therein; and a tube having a vapor line connecting with a first end of the container and a liquid line connecting with an opposite second end of the container, the channels communicating with a space defined between the inner surface of the container and the wick structure, the space communicating with the vapor line of the tube.
 12. The heat pipe as claimed in claim 12, wherein the second wick portion comprises a central portion and a number of ribs extending outwardly from a periphery of the central portion, and the outmost end of the ribs abut against the first wick portion.
 13. The heat pipe as claimed in claim 13, wherein the ribs are spaced from each other and each of the channel is defined between two adjacent ribs.
 14. The heat pipe as claimed in claim 13, wherein a receiving chamber is defined in the central portion of the second wick structure along a longitudinal direction of the central portion to receive liquid working medium therein, the receiving chamber being surrounded by the channels.
 15. The wick structure as claimed in claim 12, wherein the wick structure consists of porous structure.
 16. The wick structure as claimed in claim 16, wherein the first and second wick portions have the same porosity.
 17. The wick structure as claimed in claim 16, wherein a porosity of the first wick portion is larger than that of the second wick portion. 